1. Field of the Invention
This invention relates generally to systems and related methods for producing three-dimensional objects out of a medium capable of physical transformation upon exposure to synergistic stimulation and more specifically, for producing three-dimensional objects out of sheets or films of the material corresponding to cross-sections of the object.
2. Background of the Invention
Stereolithography is a process for building up an object layer by layer such that the layers are sequentially formed adjacent to one another until the overall production is complete. The stereolithographic production is commonly referred to as a stereolithographic object or part, or more simply, part. The process is described in more detail in U.S. Pat. No. 4,575,330, entitled "APPARATUS FOR PRODUCTION OF THREE-DIMENSIONAL OBJECTS BY STEREOLITHOGRAPHY," by Charles W. Hull, which issued Mar. 11, 1986, and which is hereby fully incorporated by reference herein as though set forth in full. As described in U.S. Pat. No. 4,575,330, a stereolithographic apparatus ("SLA") is an apparatus for producing an object through the process of stereolithography. One embodiment of an SLA comprises synergistic stimulating means such as a UV laser or the like for producing a UV-beam of synergistic stimulation, a material such as a photocurable liquid resin placed in a vat, which is capable of physical transformation upon exposure to synergistic stimulation, and an elevator means. This SLA forms each layer of a part by tracing the cross-sectional pattern on the surface of the material with the UV laser beam at an exposure sufficient to cure the liquid resin to a predetermined thickness beyond the surface.
The elevator means supports the part as it is being built up, with the first layer of the part adhering to and being supported by cured resin in the shape of webs or the like, known as a base or support, which base or support, in turn, directly adheres to the elevator means. Subsequently formed layers are then stacked on top of the previously formed layers. As the part is being built up, the elevator means progressively lowers itself into the vat of liquid resin. At each step of the way, after a layer has been formed, the elevator means lowers that layer (along with all the other formed layers) into the vat of liquid resin so that fresh liquid resin, that will be used to form the next layer, flows over the previous layer. Typically, the elevator means is lowered into the liquid resin by more than the desired thickness of the next layer so that the liquid resin will flow over the previous layer rapidly. This results in excess resin (resin of greater thickness than the next desired layer thickness) coating over at least a substantial portion of the previous cross-section. The elevator means is then raised and one or more techniques of decreasing the excess resin thickness are implemented so that a coating thickness of depth substantially equal to the next desired layer thickness is achieved. At some point during the process, the upper surface of the previously cured cross-section is positioned to be a depth below the desired liquid surface (known as the working surface) substantially equal to the next desired layer thickness. This process prepares the surface of the resin and position of the previous layer for exposing the next cross-section and adhering it to the previous layer. The various methods of decreasing the thickness of the excess resin are disclosed in several of the following co-pending patent applications. Alternatively, the material level may be raised as opposed to the part being lowered or a combination involving both techniques may be used.
For further details on stereolithography, reference is made to U.S. Pat. 4,575,330 and the following pending U.S. and international patent applications, which are incorporated herein by reference in their entirety, including appendices attached thereto or material incorporated therein by reference, as if fully set forth:
______________________________________ U.S. Pat. application Filing Ser. No. Date Inventor(s) Status ______________________________________ 07/183,021 4/18/88 Freed Abandoned 07/182,823 4/18/88 Hull et al. Abandoned 07/182,830 4/18/88 Hull et al. U.S. Pat. No. 5,059,359 07/183,016 4/18/88 Modrek U.S. Pat. No. 4,996,010 07/183,014 4/18/88 Hull Abandoned 07/182,801 4/18/88 Hull et al. U.S. Pat. No. 4,999,143 07/183,015 4/18/88 Smalley U.S. Pat. No. 5,015,424 07/268,428 11/8/88 Freed Abandoned 07/268,408 11/8/88 Hull Abandoned 07/268,429 11/8/88 Modrek et al. U.S. Pat. No. 5,076,974 07/268,816 11/8/88 Spence U.S. Pat. No. 5,058,988 07/268,837 11/8/88 Spence et al. Pending 07/268,907 11/8/88 Spence et al. U.S. Pat. No. 5,059,021 07/331,644 3/31/89 Hull et al. Pending 07/339,246 4/17/89 Hull et al. Pending 07/365,444 6/12/89 Leyden et al. Pending 07/414,200 9/28/89 Hull et al. Pending 07/415,168 9/29/89 Hull et al. Pending 07/429,911 10/27/89 Spence et al. Pending 07/427,885 10/27/89 Spence et al. Pending 07/429,435 10/30/89 Smalley et al. Pending 07/429,301 10/30/89 Lewis et al. Abandoned 07/495,791 3/19/90 Jacobs et al. Pending 07/515,479 4/27/90 Almquist et al. Pending 07/545,517 6/28/90 Cohen U.S. Pat. No. 5,096,530 07/566,527 8/13/90 Jacobs et al. Abandoned ______________________________________
In the above described embodiment using a liquid photopolymer, because of the viscosity of the liquid resin, the time required to coat a previous layer of the object with a fresh layer of liquid resin in preparation for formation of the next layer can be prohibitively long. This is explained in more detail in U.S. patent application Ser. No. 07/515,479, referenced earlier. Therefore, a need exists for more rapidly delivering a fresh layer of material resin to a previous object layer.
In addition, as explained in more detail in U.S. patent application Ser. Nos. 339,246; 183,015; and 182,801, liquid resin generally shrinks when it solidifies upon exposure to UV radiation or other synergistic stimulation, and this shrinkage may result in distortion of the resultant object. To minimize this shrinkage and resultant distortion, the above embodiment preferably employs a beam of synergistic stimulation which is directed to trace, and therefore sequentially solidify, only a small portion of each layer at a time. By sequentially solidifying each portion of a layer, fresh liquid resin will be allowed to flow into the voids caused by shrinkage, and thereby reduce distortion. A problem with sequentially solidifying each layer, however, is that layer solidification will take more time than if selective flood exposure to the synergistic stimulation were employed. Therefore, a need exists for employing flood exposure of the synergistic stimulation to solidify a layer without introducing excessive distortion into the object.
Also, with current resins, layer thicknesses less than about 5 mils are difficult, if not impossible to achieve, which limits the vertical resolution of the part. Therefore, a need exists for building parts with smaller layer thicknesses.
Finally, preferred commercial methods of part building are directed to the use of flowable building materials such as photopolymers. Other flowable materials include powdered materials that are solidified by sintering or by selective dispensing of chemical agents such as binders or the like. A need exists to expand the range of materials which can be used to build three-dimensional objects, such as metals or other materials.
Accordingly, an object of the subject invention is to decrease the time required to coat a previous layer of the object with a fresh layer of material in preparation for formation of the next layer of structure. Another object is to decrease the time required to expose the fresh layer to synergistic stimulation without increasing distortion caused by shrinkage of the material upon exposure to the synergistic stimulation. Additional objects are to decrease the layer thickness achievable, and to expand the range of materials which can be used in three-dimensional part building.
Additional objects and advantages of the invention will be set forth in the description which follows or will be apparent to those of skill in the art who practice the invention.